According to survivors of the massacre, the attackers claimed repeatedly to be Taliban and al Qaida. One of the attackers said that the murders were in revenge for the killing of Osama bin Laden by the US. Tehrik-i-Taliban Pakistan - a Pakistan-based umbrella organisation distinct from the Afghan Taliban - subsequently claimed responsibility, saying that the attack was a response to US drone strikes. Another group - Jundallah - also claimed responsibility, saying simply "these foreigners are our enemies".

Only one of victims - Honglu Chen - was American. He was a dual US and Chinese national. The other victims were Igor Svergun (Ukraine), Kashaev Magomedovich Badawi (Ukraine), Konyaev Dmitry Sergeyevich (Ukraine), Rao Jianfeng (China), Yang Chufeng (China), Ernestas Marksaitis (Lithuania), Sona Sherpa (Nepal), Anton Dobes (Slovakia), Peter Sperka (Slovakia) and Ali Hussain (Pakistan). Ali Hussain was working as a cook with one of the various expeditions. He was probably killed because he was thought to be a Shia.

Nanga Parbat (8126m) is the ninth highest mountain in the world and is the apex of an isolated knot of mountains at the western extremity of the the Himalaya Range, in the Gilgit-Baltistan area of Pakistan. The Karakoram mountains stand to the north and east, separated from Himalaya by the River Indus. As the crow flies, the summit of Nanga Parbat is hardly more than 20 kilometres from the Karakoram Highway. The India-controlled Vale of Kashmir lies 100 kilometres to the south.

Diamir Base Camp is situated at an altitude of about 4100m beneath the west face of Nanga Parbat. The trek to the Base Camp is generally done in two days from the roadhead in the Diamer (Diamir) Valley, which is reached from the Karakoram Highway. Some media reports have confused Diamir Base Camp with Rakhiot Base Camp and Fairy Meadow on the northern side of the mountain, which has a somewhat easier approach.

The attack seems to have been carried out by a group of about 15 militants, disguised in army or police uniforms (some reports say they were wearing the uniforms of the Gilgit Scouts, a unit of the Pakistan Army). The disguises may hardly have been necessary. It seems that it is normal for visitors to travel through the area without encountering security personnel.

According to some reports, the attackers abducted two local people to guide them to the Base Camp. These reports should be treated with caution, since the same reports said that one of the abducted guides was killed - a claim which does not tally with the published list of the dead.

"Taliban! Al Qaeda! Surrender!"

On the night of 22 June, climbers from several different expeditions were at the Base Camp. The attackers burst upon them at around 9.30pm , brandishing Kalashnikovs and shouting "Taliban! Al Qaeda! Surrender!"

People were tied up. Money was collected. Mobile phones, walkie-talkies and laptops were collected and destroyed. And then the execution-style shootings began.

Pakistani climber Sher Khan was spared, once it was established that he was Muslim, albeit an Ismaili from Hunza. Two other Ismailis from Hunza were spared too. It also appears that about a dozen local expedition staff were tied up in their tents but were not killed.

A Chinese climber, Zhang Jingchuan, somehow survived the first shots and then ran for his life. He had served in the army and he put his training to good use, running in zigzags and rolling over to escape the bullets until he could hide on the glacier a little way from the camp.

Later that night, Zhang Jingchuan crept back into camp, found his satellite phone and contacted his trekking agency in Nepal, who then contacted Nazir Shabir, the owner of a Pakistani company that had arranged one of the expeditions to the mountain. Nazir Shabir in turn contacted the Pakistani authorities.

Zhang Jingchuan recovered his warm clothes and an ice axe and then escaped up the mountain, feeling safer there than in the camp.

Once the attackers appeared to have gone, Sher Khan and his two friends from Hunza freed themselves using a knife from the kitchen tent. They searched for a satellite phone without success, but found two walkie-talkies. Fearful that the attackers would return, and still without warm clothes or mountaineering boots, they climbed to a point about 300 metres above the camp, where they found shelter.

Eventually, at about 7.30 the next morning, they were able to make contact over the walkie-talkie with one of the other camps, who in turn contacted Nazir Sabir. He told them that the authorities had already been alerted - presumably as a result of Zhang Jingchuan's call - and that army helicopters were on the way.

The survivors were evacuated by air. Climbers who were higher on the mountain returned to Base Camp and were evacuated later.

"These foreigners are our enemies"

On 23 June Reuters news agency reported that the Jundallah group had claimed responsibility for the attack. Jundallah spokesman Ahmed Marwa said:

"These foreigners are our enemies and we proudly claim responsibility for killing them, and will continue such attacks in the future".

Jundullah has a history of carrying out attacks against Shia in Pakistan. It seems to be a separate organisation from the group of the same name that that has carried out acts ot terrorism in Iran. The Iranian group often operates from Pakistani Balochistan.

“One of our factions, Jundul Hafsa, did it to avenge the killing of Maulvi Waliur Rehman.”

Rehman was one of between 3 and 7 people killed in a US drone strike in North Waziristan (in Pakistan's Federally Aministered Tribal Areas Pakistan) on 29 May. It was the first such strike after a 42-day respite that coincided with Pakistan's elections. Further US strikes in June and July are reported to have killed between 31 and 38 people in North Waziristan. An estimated 2500 to 3500 people - 164 to 195 of them children - have been killed by US drone strikes on Pakistan since 2004.

The Taliban spokesman said that Jundul Hafsa was a new wing set up by the Taliban “to attack foreigners and convey a message to the world against drone strikes”.

The claims from Jundullah and the Taliban may both be correct. The relationship between the two organisations is unclear. A bomb attack in Sukhur, in Pakistan's Sindh Province, on 24 July was attributed by some media sources to "Tehrik-i-Taliban Pakistan Jundullah", but it was also reported that a TTP spokesman, while claiming responsibility, had disputed Jundullah's claim.

Tehrik-i-Taliban Pakistan was set up in December 2007 as an umbrella group unifying various militant groups operating in Pakistan's Federally Administered Tribal Areas (FATA) and in Khyber Pakhtunkhwan province. The new organisation was part of an upsurge of militant activity that followed the storming of the Lal Masjid in Islamabad by Pakistani security forces in July 2007, which resulted in many deaths amongst radical students based there. It was perhaps also a response to the Pakistan Government's strategy of striking separate deals with the various militant groups.

The groups that created TTP had helped support the Afghan Taliban when the latter escaped into Pakistan after the US assault on Afghanistan in 2001. But many of the Pakistani groups were not themselves precisely "Taliban" - their background was with networks created during the Afghan struggle against Soviet occupation in the 1980s.

Nevertheless, TTP has consistently said that it regards the Afghan Taliban leader Mullah Omar as the overall leader of the Taliban movement. Its founding meeting declared that its aim was to "unite the Taliban against NATO forces in Afghanistan and to wage a defensive jihad against Pakistani forces here [FATA/Pakistan]."

Some Taliban factions believe TTP's war on the Pakistani state to be a strategic mistake. Taliban leader Maulvi Nazir, assassinated in a US drone strike in January, had maintained cordial relations with the Pakistani army and focussed his own forces on support for the war against NATO forces in Afghanistan.

Faced with US drone attacks and Pakistani military action, TTP has been unable to consolidate its hold on the FATA/Khyber Pakhtunkhwan region, but on the other hand it has gained new support elsewhere in Pakistan, especially Punjab.

Exploiting sectarianism

Tribal loyalties are the glue that holds the TTP together in the north-west, but in Punjab and elsewhere it has had to exploit religious sectarianism to attract supporters. The main Punjab groups allied to TTP all have a prior history of violence towards Shia Muslims. Inevitably, this is reinforcing anti-Shia sectarianism back in the TTP heartlands.

Pakistan is overwhelmingly Sunni. But Gilgit-Baltistan, the self-governing region where Nanga Parbat stands, has a rather different make-up. At the 1998 census, only 27% of the population of the region were Sunni. The proportion may be higher now, inflated by the steady trickle of Punjabis and Pashtuns into the area.

39% of the of Gilgit-Baltistan population were recorded in the census as Shia, 16% as Nurbakhsha - a Sufi order generally regarded as Shia - and 18% as Ismaili - also a branch of Shia Islam.

Shias are often said to total three quarters of the population of Gilgit-Baltistan. This seems to be rather a simplification. Ismailis have often been able to stand apart from Sunni-Shia sectarianism, as the climber Sher Khan and his two friends found when they were taken out of the execution line at Diamir Base Camp. But on other occasions both Sunnis and Shias have accused Ismailis of belonging to the opposing camp. And efforts have been made to convert Nurbakhshas by both Sunnis and Shias.

Religious sectarianism seems to have played little part in regional life when Gilgit-Baltistan was part of the princely state Jammu and Kashmir, a franchise of the British Empire. But tension and conflict have grown since the region became part of Pakistan in 1947.

The situation worsened in the 1980s when the Zia dictatorship attempted to impose Sunni Islamic law in Shia-majority areas, and deteriorated further with the creation of camps where Sunni militants were trained for combat in Indian-controlled Kashmir and Soviet-occupied Afghanistan. Many young men from the Diamer (Diamir) district took part in the training.

Some of the militant groups operating in Kashmir from Gilgit-Baltistan bases - with the support of the Pakistani government - were fiercely anti-Shia.

Sectarian tension in Gilgit-Baltistan wasn't an unintended consequence of Pakistan's cross-border adventures. On the contrary, successive governments used sectarianism to help maintain control over the region.

The fruits of this policy have been bitter and spectacular. Anti-Shia riots in 1988 culminated in the invasion of the area, under the noses of the security forces, by an 80,000 strong 'army' of Sunni thugs. Shia villages were destroyed and hundreds of Shia were killed.

The murder of a prominent Shia leader in Gilgit in 2005 provoked anti-Sunni riots which were contained by the imposition of a month-long curfew in Gilgit and Skardu.

Attacked on the Karakoram Highway

For a number of years Shia have been subject to attacks while travelling the Karakoram Highway in Gilgit-Baltistan and in Kohistan, the adjoining district of Khyber Pakhtunkhwan province.

A military offensive in 2009 against the Taliban in the Swat Valley of Khyber Pakhtunkhwa displaced over 2 million people. Many fled to temporary camps elsewhere in Khyber Pakhtunkhwa and have now returned to their homes. Some are said to have settled in the Diamer area of Gilgit-Baltistan. Whether or not they include Taliban militants, as has occasionally been rumoured, their arrival is likely to have heightened sectarian tension.

In April 2012, hand grenades were thrown at Sunni activists in Gilgit who were protesting at the arrest of a Sunni leader in connection with sectarian killings in Kohistan. Shooting then broke out in various parts of the town.

Later that day, near Chilas - the administrative headquarters of Diamer district - buses were stopped and Shia passengers were taken off them and killed. Details of the attack are unclear, with some sources claiming that the Pakistani media were encouraged by the military to downplay the incident. Pakistan's Dawn newspaper reported that the Chilas attack was carried out by a mob "tens of thousands" strong and that nine Shia were killed. There are rumours that the death toll was much higher. According to some reports, the lives of many Shia were saved by local Sunnis who took them under their protection.

Sunni mosques made announcements against the Shia community. In Hunza, Shias responded by taking 34 Sunnis - including a civil judge - hostage. The hostages were eventually released unharmed. The army imposed a curfew in Gilgit. Mobile phone services were jammed. The Karakoram Highway was effectively closed. Across the border in Kargil, in India-controlled Kashmir, the Shia community organised a strike and shut-down in protest against the killings in Pakistan.

In August there was another attack on Shia bus passengers travelling through Kohistan to Gilgit. The attackers wore military uniform and tied their victims up before shooting them. TTP claimed responsibility for the massacre and promised more such attacks. Renewed violence broke out in Gilgit in response to the killings, and a curfew was once again imposed.

"If the murderers of the Shias had been caught and sentenced last year, perhaps those mountaineers would have still been alive today."

Arrests

At least 30 people were arrested shortly after the Nanga Parbat massacre. They appear to have been people thought likely to provide information, rather than genuine suspects.

Within a few days, the police announced that they had identified the attackers. Ten named suspects were said to be from the Diamer Valley, three were said to be from Mansehra, in Khyber-Pakhtunkhwa, and another three were said to be from Kohistan, also in Khyber-Pakhtunkhwa.

On 15 July, Pakistan's Senate Standing Committee on Foreign Affairs was told that four suspects had been arrested and that a breakthrough was expected within 7 days. There has been no further news.

It would be unwise, for the moment, to take the police identification of the attackers too seriously.

Update 19 August 2013: Police in Pakistan say they have arrested 20 suspects in connection with the massacre and with sectarian murders. The suspects will be tried in Diamer district court.Nanga Parbat murder suspects arrested

The announcement by the police follows a military operation in Chilas earlier in August apparently conducted in order to detain the suspects. An army colonel, a captain and a senior superintendent of police (SSP) investigating the killings had previously been murdered near Chilas.Army operation in Chilas.

After the Nanga Parbat massacre a number of people, their eye no doubt on the tourist business, insisted that Gilgit-Baltistan is a peaceful area. That's a historical and aspirational statement, not a description of present-day reality.

The massacre was remarkable only because the victims were mostly foreigners, and because of the altitude at which it was carried out.

None of the victims had any role in the US war on the Taliban. None of them were legitimate targets for the Taliban. But the massacre wasn't irrational.

Whether or not the attack puts pressure on the international community - the declared aim of the TTP - it will certainly put pressure on the Pakistani government.

The terrorist attack on the Sri Lanka cricket team in Lahore in 2009, which left eight people dead, propelled Pakistan into sporting isolation. No international cricket matches have been played in Pakistan since then. No one, except perhaps for TTP and its allies, wants mountaineering and mountain tourism, let alone the tourist industry in general, to make a similar exit from Pakistan.

The men who carried out the Nanga Parbat attack would perhaps have preferred to catch more Americans. But the inclusion of Chinese citizens among their victims will ensure that they get the attention of the Pakistani Government. A Chinese company is currently at work on repairs to the Karakoram Highway under the protection of a specially-created unit of the Gilgit-Baltistan police.

China's Economic Corridor

China is a key ally of Pakistan and will become an increasingly important power-broker as US troops withdraw from Afghanistan.

In Xinjiang Province, across the border from Gilgit-Baltistan, China is confronting a separatist movement amongst Uyghur Muslims. Uyghurs have suffered serious human rights abuses, including torture and arbitrary detention, at the hands of the Chinese authorities. The frontier areas of Pakistan are a potential source of support for Uyghur rebels.

On 5 July China and Pakistan reached agreement on a futuristic plan for an "economic corridor" running from Kashgar in Xinjiang, along the Karakoram Highway and down to Gwadar, a Pakistani port currently operated by a Chinese state-run company. The deal includes plans for 200 kilometres of tunnels. Fibre-optic cables will bring high-speed internet connections into the area, and there may eventually be a rail link.

The Taliban offensive has continued through July. There was a bomb attack on offices of Pakistan's intelligence agency in Sukkur, in the south of Pakistan. A daring Taliban attack on a jail in Dera Ismail Khan, in Khyber-Pakhtunkhwa, freed hundreds of prisoners. A bomb attack on a market in Parachinar, in FATA, killed at least 57 people, most of them Shia. The spokesman for the newly-formed group that claimed responsibility for the attack said it was retaliation for drone strikes and for "the atrocities committed against the majority Sunni population in Iraq and Syria".

Drones crawl endlessly across the skies of South Waziristan. It is as if a known suicide bomber were driving around your streets all day, back and forth, past houses and shops and schools.

UN Secretary-General Ban Ki-moon says that the use of “armed and surveillance drones has resulted in permanent fear in some communities, affecting the psychosocial wellbeing of children.”

Pakistan's newly-elected Pakistani Prime Minister Nawaz Sharif used his inaugural address to the National Assembly on 5 June to call for an end to US drone strikes. The US answered on 8 June with a drone attack in South Waziristan. The Pakistani Foreign Office summoned the US Ambassador and told him that "the Government of Pakistan strongly condemns the drone strikes which are a violation of Pakistan’s sovereignty and territorial integrity." More drone strikes followed.

Pakistan's previous government had also called for an end to drone strikes, without apparent effect.

The Taliban seem to be trying to put pressure on the Pakistani government to act firmly to stop drone strikes. It would be a commendable aim, were it not for the filthy strategy through which the TTP is pursuing it. The same filthy strategy would be just as serviceable to anyone else who wished to undermine the Pakistani Government.

That could include any sections of the Pakistani military who still bear a grudge against Nawaz Sharif. His attempt, last time he was in office, to hold the army to account for its disastrous 1999 incursion into the Kargil district in India-controlled Kashmir was brought to an end by a military coup.

It could also include anyone who wishes to widen the gap between Pakistan and the Afghan Taliban.

TTP is not a tool of either the CIA or the Pakistani military. But sections of the Pakistani military might be amongst the influences that play upon some groups aligned with TTP.

It's an intriguing dance, seen from afar. Up close, on the Karakoram Highway or the slopes of Nanga Parbat, it is bloody, despicable, putrid.

The Pakistani authorities have been quick to say that they will take action to ensure the safety of visiting mountaineers. It should be possible to improve on the non-existent security in the valleys around Nanga Parbat, but it might not be easy to make the security truly effective.

How many guards would it take to protect a mountaineering Base Camp? And why should climbers come to Pakistan to spend their holiday under armed guard, like the Chinese road-builders? What about the trekkers who walk freely through the area?

"If we send one or two officials to accompany the expedition teams for their security, the officials demand dollars from the foreigners and then come back after barely crossing the last village from where the mountains start."

He also said that police sent to investigate the massacre had failed to reach the Base Camp due to the effects of altitude.

Military personnel could be expected to perform better. But militarising security in the Nanga Parbat area might create new problems.

In the Karakoram mountains on the other side of the Indus, the situation is different. Numerous groups, large and small, visit the area.

Safety in the Karakoram?

The highest mountains are situated in a restricted zone along the Chinese border. Climbers attempting these peaks must be accompanied by a liaison officer from the Pakistani military. There is no such requirement on trekkers who visit the restricted zone.

The approaches to the peaks are generally longer and more glaciated than the trek to Nanga Parbat. It's difficult to guess how serious the risk of a Taliban attack might be in this area.

Perhaps TTP militants would find it harder to operate in the mainly Shia valleys around Skardu than amongst the Sunnis of the Diamir area. Perhaps not. Perhaps the approaches to the mountains are too arduous, or would expose attackers to the risk of discovery for too long. Perhaps not.

In the east of the area, the Pakistani army is locked into a long stand-off with the Indian army on the Siachen Glacier. Tribal militias and Islamic militants have been allies of the Pakistani army throughout its struggle with India, starting with the India-Pakistan War of 1947. Perhaps soldiers and militants will avoid confronting each other under the noses of their old enemy. Perhaps not.

No one expected the Nanga Parbat attack. The dangers that were brewing there are now clear to everyone, but they were not clear beforehand. There is no good reason to believe that visitors to the Karakoram are safe from a similar attack.

But in any case, there is no need for TTP militants to tramp the mountains in pursuit of foreigners. They can find them easily enough in the cities if they wish to do so.

Religious sectarianism and anti-foreigner sentiment are interconnected. Tehrik-i-Taliban Pakistan has decided that they both suit its purpose. So Pakistan has become a more dangerous place. Strengthened security measures will not create much real security. On the other hand, all the players on Pakistan's political stage could take steps to improve the situation.

The police could conduct a thorough investigation into the Nanga Parbat massacre, gather solid evidence, and bring those they believe responsible before a court.

Tehrik-i-Taliban Pakistan and its allies could strike sectarian and anti-foreigner violence off their playlist. The US could stop its drone attacks. The Pakistani Government could tackle religious sectarianism right across the country. It could foster democratic decision-making in Gilgit-Baltistan, instead of using sectarianism to stalemate it.

The withdrawal of US troops from Afghanistan, if it really happens, will create an opportunity for Pakistan to heal its wounds. But it's an opportunity that could easily slip by, unused.

As for travellers and mountaineers - if you go to Pakistan, take care.